A dielectric layer is an important component in the manufacture of integrated circuits. A dielectric is used generally to electrically isolate conductive layers and enable useful interconnects between such layers. As device densities increase, multiple dielectric layers may be used to isolate stacked device features. When forming such multilayer dielectric it is desirable to provide a dielectric film with good gap fill, isolation, stress and step coverage properties on patterned material layers. These properties become critical as device dimensions shrink.
Dielectric layers are often formed by Chemical Vapor Deposition (CVD). The CVD process deposits a material on a surface by transport and reaction of certain gaseous precursors on such surface. Plasma may be used to assist decomposition of certain gaseous chemicals. CVD apparatus come in many forms. Low pressure CVD systems and atmospheric pressure CVD systems operate on thermal CVD principles. Plasma CVD systems operate by disassociation and ionization of gaseous chemicals and are able to operate at lower temperatures than conventional thermal CVD systems. Such lower temperature methods are desirable and will minimize diffusion of shallow junctions and inter-diffusion of metals.
In addition to good gap fill and step overage properties it is desirable to provide a dielectric layer with a low dielectric constant. As the intra-layer metal width and spacing of the interconnections decrease, the wiring (or sometimes referred to as line-to-line) capacitance increases and becomes the major factor contributing to the total capacitance. Another factor contributing to the total capacitance, but to a lesser extent, is the inter-layer capacitance. The total capacitance, limits the operating speed of such devices. A layer with a low dielectric constant provides an immediate performance improvement due to a reduction in capacitance.
It is desirable to develop a suitable method of forming a dielectric which provides low dielectric constants, having all of the necessary film properties such as stability, density, gap fill, low film stress and step coverage.